1. Field of the Invention
This invention relates generally to the field of drilling. More specifically, the invention relates to a method of analyzing distributed measurements in drilling.
2. Background of the Invention
During drilling operations, measurements of downhole conditions taken in-situ provide valuable information that can be used to optimize drilling practices, enhance operational efficiency and minimize operational risk. These direct measurements can also help to provide a near real time picture of changing trends down hole that can help to allow detection of developing problems in the well. The interest primarily arises from the fact that even minor interruptions in drilling operations can be exorbitantly expensive. Thus, drilling companies have a strong incentive to avoid interruptions of any kind.
Gathering information about down-hole drilling conditions, however, can be a daunting challenge. The down-hole environment is very harsh, especially in terms of temperature, shock, and vibration. Furthermore, many drilling operations are conducted very deep within the earth, e.g., 20,000′ 30,000′, and the length of the drill string causes significant attenuation in the signal carrying the data to the surface. The difficulties of the down-hole environment also greatly hamper making and maintaining electrical connections down-hole, which impairs the ability to obtain large amounts of data down-hole and transmit it to the surface during drilling operations.
Approaches to these problems are few in terms of assessing adverse downhole drilling conditions. Non-threatening conditions may be recorded, displayed, or analyzed by a computing device as well. In general, data taken from the surface and only limited data taken from the surface and/or the bottom of the borehole is available. The drilling operators must extrapolate the down-hole drilling conditions from this data. Because the borehole might be as deep as 20,000′ 30,000′, surface data frequently is not particularly helpful in these types of extrapolations. The down-hole data can be more useful than surface data, but its utility is limited by its relatively small amount and the fact that it represents conditions localized at the bottom of the bore. Thus, the down-hole data may be useful in detecting some conditions at the bottom of the borehole but of little use for other conditions along the length of the drill string.
There are significant technical challenges both to gathering data in the downhole environment and also to communicating this data to engineers at the well site or in the office. These problems are exacerbated in very long (extended reach) or very challenging (so called high temperature high pressure) wells. Conventional pressure pulse data transmission suffers both from a significant restriction in the volume of data that can be transmitted to surface, the incremental time taken to transmit and the fact that reliability decreases with increased well depth due to reduction in amplitude of pressure waves as they move up the well.
In drilling operations making use of mud pulse telemetry measurements are taken both down hole and at surface. Surface measurements can be split into instantaneous and lagged while down hole measurements are near instantaneous. Lagged data received at surface refers to measurements made or information inferred from drilling fluid that has been circulated to the surface and can include measurements such as gas concentration, volume of drilled solids carried or mud density. This lagged data takes a significant time to retrieve due to the time required to circulate drilling fluid from the bit to surface and as such is only useful for retrospective analysis. Down hole measurements are more useful but limited in how much of the measured data can be transmitted to surface and also in that there is only a single measurement point usually at the very bottom of the well. In the case of pressure this provides valuable information about the entire fluid column in the annulus but cannot be used to determine the location of any detected anomalies in the annulus we know only that something has happened between surface and the sensor.
One example of an application of downhole monitoring of conditions in down-hole drilling applications are the use of drilling fluids. Drilling fluids (muds) are circulated through the drill string and annulus of the borehole to remove cuttings from the well, lubricate and cool the drill bit, stabilize the well bore walls, prevent undesired influxes by countering formation pore pressure, and the like. The drilling fluid also facilitates removal of cuttings as result of drilling.
Indications that cuttings beds are forming in the well bore can be garnered through increases in torque and drag as well as a reduction in the volume of cuttings seen at surface. Currently however there is no certain method of determining in which regions of the well these beds are forming. The ability to take measurements at multiple points along the well simultaneously and in real time, as well as accelerate data transmission and increase volume of data from BHA conveyed tools that is seen at surface has the potential to increase accuracy and speed of diagnosis of down-hole events in real time.
Accordingly, the use of distributed sensors along the drill string and distributed measurements provides many advantages previously not feasible with existing technologies. However, beyond the basic concept of using distributed measurement data for cuttings loadings, detailed methods for doing so and applications for assessing other borehole conditions have not yet been disclosed with respect to distributed measurements.
Consequently, there is a need for methods of determining borehole conditions using distributed measurement data along the drill string.